The present invention relates to a mobile lifting crane that uses multiple hoist drums. These hoist drums may include load hoist drums, such as for lifting a load and an auxiliary or whip line, and boom hoist drums, such as for changing the angle of the boom and changing the angle of a luffing jib.
Mobile lift cranes typically include a carbody having moveable ground engaging members; a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members; a boom pivotally mounted on a front portion of the rotating bed, with a load hoist line extending there from, and counterweight to help balance the crane when the crane lifts a load. Many large capacity cranes include more than one load hoist drum, such as a second main hoist line and an auxiliary or whip line.
There are different ways of changing the angle of the boom with respect to the rotating bed during crane operation, including using hydraulic cylinders mounted between the boom and the rotating bed. However, more commonly a boom hoist drum and rigging are used to change the boom angle. Many cranes also use a mast mounted on the rotating bed to support the rigging, including the boom hoist rigging, so that it may transfer the forces from lifting a load to the rear of the carbody and the counterweight. The boom hoist rigging must carry large tension loads, supporting not only the boom, but counteracting the angled force applied by the boom as it supports the load. The boom hoist rigging includes the boom hoist line extending from the boom hoist drum and reeved through a lower equalizer (which may be attached to the top of the mast), and an upper equalizer with multiple parts of line so that the large tension loads on the rigging are distributed over the multiple parts of line. If the crane is equipped with a luffing jib, the crane will also normally include another boom hoist drum to spool the wire rope used to control the angle of the luffing jib. Thus a large capacity crane may be equipped with four or five hoist drums.
Since the crane will be used in various locations, it needs to be designed so that it can be transported from one job site to the next. This usually requires that the crane be dismantled into components that are of a size and weight that they can be transported by truck within highway transportation limits. For very large cranes, this may require taking the hoist drums off of the rotating bed. The ease with which the crane can be dismantled and set up has an impact on the total cost of using the crane. Thus, to the extent that fewer man-hours are needed to set up the crane, there is a direct advantage to the crane owner. Thus it is beneficial, if the hoist drums are removed, to be able to leave the line on the drums, and to the extent possible, leave the line reeved though as many sheaves as is possible.
Further, when there are a large number of hoist drums on the rotating bed, the rotating bed is typically rather long to provide space for mounting the drums, as well as the other major crane components that are mounted on the rotating bed, such as the mast, the boom stop and any mast stop or backhitch. However, a long rotating bed has disadvantages, primarily because it increases the tail swing of the crane when the crane is being repositioned on the job site. Also, a long rotating bed will inherently have increased weight and manufacturing costs, and may cause additional difficulties if the length exceeds highway transportation limits. Some crane manufacturers have resorted to mounting hoist drums on the boom or mast in order to avoid having a long rotating bed. However, this solution may not be entirely satisfactory, as the hydraulic lines supplying the hoist motors then have to run up the boom or mast, and the drums are harder to access for needed service.
Thus it would be a great advantage if a system could be developed that allowed for a multiple hoist drums to be included on the rotating bed without increasing the length of the rotating bed.